Perplexus - A forum and collection of brain teasers, logic problems, math problems, paradoxes, science games, probability, riddles, and geometric shapes. The puzzles are searchable and categorized, most have solutions. The Monty Hall Problem - A probability theory puzzle with solutions. [English and German.] WU Forums - Discussion board hosted at Berkeley with talk about a variety of solved and unsolved brain teasers. Monty Hall Game - JavaScript example of the Monty Hall Game. This game demonstrates the real (empirical) affect of statistics. [Does not display correctly in all browsers.] CellFighter - Shareware game based around an extension of the game of life. Two Envelope Paradox - Solution - Claims that the two envelope paradox comes from the incorrect use of probabilities. Mathematical Puzzles - Number puzzles with various levels of difficulty and solutions. Includes printable versions. IBM Research: Ponder This - Monthly logic and math puzzles set by IBM researchers with solutions.